1. Field of the Invention
The present invention relates to an output driver, and particularly relates to an output driver of a memory.
2. Description of the Prior Art
Since the performance of modern processors is continuously improving, the memory bandwidth becomes a critical characteristic affecting the performance of a computer system. The technique of Double-Data-Rate (DDR) memory has developed from DDRI to DDRII and through to the newest: DDRIII. Each standard, however, has specific requirements. According to the DDR standard determined by JDEC, DDRI memory must follow the SSTL-25 standard, where the voltage on the I/O port of the memory must be 2.5 V. DDRII memory must follow the SSTL-18 standard, where the voltage on the I/O port of the memory must be 1.8 V. DDRIII memory must follow the SSTL-15 standard, where the voltage on the I/O port of the memory must be 1.5 V.
Therefore, the width of a transistor and I/O pad area must be increased for meeting different standards, so the total area of a circuit and the cost thereof are increased. Also, different voltages or different circuits must be provided if memories of different standards need to be supported. Accordingly, the inconvenience of designing, and related costs, are increased.